A battery module has a configuration in which a plurality of secondary batteries are serially connected.
A battery measures voltages of the secondary batteries of the battery module and adjusts the voltages or amounts of charge.
In order to adjust a voltage or an amount of charge of a secondary battery, it is necessary to calculate a resistance value of a wire connected to the secondary battery in advance.
Some conventional methods of calculating a resistance value of a wire use voltages which are measured before and after a current flows in a circuit.
However, since a resistance value of an internal resistor of a battery is too small and is thus ignored, the resistance value of the internal resistor is not considered when calculating the resistance value of the wire.
Accordingly, in the conventional methods of calculating a resistance value of a wire, it is not possible to calculate an accurate resistance value of a wire.